Shape memory alloy tufted composites combining high delamination resistant and crack closure properties

A new type of fibre reinforced polymer composite is presented that uniquely combines high delamination resistance with crack closure properties via the use of tufted shape memory alloy (SMA) filaments. A carbon-epoxy laminate was tufted in the through-thickness direction using thin SMA filaments of Ni-Ti alloy (nitinol). The SMA tufts increase the mode I interlaminar fracture toughness of the laminate by forming a large-scale bridging process zone along the delamination crack. Following crack growth, electrical heating of the SMA tufts activates a shape memory effect that partially closes the delamination. Finite element (FE) analysis reveals that complete crack closure occurs when the SMA tufts are not deformed above the shape memory strain limit. The use of SMA tufts offers the important opportunity to produce a new class of damage tolerant composite material that both resist the opening and aid the closing of delamination cracks formed by overloading, impact or other damaging events.